Traffic recorder



April 15, 1947. c, w 2,419,099

' TRAFFIC RECORDER Filed May 2'7, 1944 Fig. 2.

7 3:00AM- 3-754. I

W J\ U Inventor: Alexander 0. We! i,

is Attorney.

Patented Apr. 15, 1947 turen TRAFFIC REfiQRDER Alexander (3. Wall, Indianapolis, Ind, assignor to General Electric Company, a corporation of New York Application May 27, 1944, Serial No. 537,594

4 Claims.

My invention relates primarily to traffic recorders and counters although it may have other uses, and its object is to provide apparatus for counting the number of vehicles passing a given point and. record their speeds. This is accomplished without in any way interfering with traffic and without the use of electrical or mechanical connections between the recording apparatus and the vehicles or the highway over which the vehicles travel. In carrying my invention into eiiect, I make use of the sound produced by a vehicle passing over a corrugated roadbed section and a sound pickup amplifying and discriminating system in which the frequency of the sound pulsations is utilized to determine vehicle speed.

The features of my invention which are believed to be novel and patentable will be pointed out in the claims appended hereto.

For a better understanding of my invention, reference is made in the following description to the accompanying drawing in which Fig. 1 represents a traffic counter and speed recorder embodying my invention; Fig. 2 indicates the nature of the record to be expected; Fig. 3 represents a timed record; and Fig. 4 indicates a roadway having sound producing means arranged for use of the invention for trafiic in opposite directions.

Referring to Fig. 1, l represents the surface of a highway over which a vehicle 2 is passing. Over a short length of the highway, such as half the length of an ordinary vehicle, the surface of the highway is provided with corrugations 3 having a uniform spacing in the direction of vehicle travel. Such corrugations may be provided in the surface of the highway when the highway surface is laid, in concrete, for example. A corrugated sheet of metal may also be used, or a corrugated mat made of rubber or the like may be laid upon and secured to the highway surface as by glue or cement. The corrugations need to extend laterally of the highway only far enough to have a wheel or wheels on one side of a vehicle pass over the same, although all wheels may pass over such corrugated surface if desired. The purpose of these corrugations is to emit sound pulsations when traversed by the wheel of a vehicle, and to produce a pulsation frequency proportional to the speed of such vehicle for a given spacing of the corrugations. The depth of the corrugations is not sufficient to slow traffic or cause any traffic hazard or discomfort. It may be necessary to remove snow or ice, where such conditions occur, in order to produce the sound effect. desired which-is caused by the vehicle wheel selected but for the" purpose of explanation the relation above mentioned will be used. It is of' course well known that when a vehicle is traveling over a highway at high speed, a variety of noises of low level are produced, but the noise produced by the corrugated surface will stand out because distinguished by a definite frequency which will for all practicable purposes be constant during the passage of a particular vehicle.

In order to pick up this distinguishing sound, a microphone 4 is provided on one side of the highway near the corrugated surface. It is contemplated that such microphone may be located a sufficient distance to the side. of the highway to be out of the way of all trafllc and may be mounted on a telephone pole or fence post, or simply laid on the ground if the use is to be temporary as in a test trafiic count. The microphone is contained in the input circuit of a vacuum tube system designed to eliminate sound frequencies other than those desired, to amplify the desired frequency pulsations and convert into electrical variations such that the number of vehicles may be counted and their speeds measured, indicated, and recorded by suitable instruments associated with the output circuit of the system. Without doubt there are a variety of vacuum tube circuits andarrangements that might be used for this purpose, and I do not wish to limit my invention to the particular one represented.

The microphone is shown connected in series with a battery 5, a condenser 6, and a resistance 1, such that a pulsating voltage will be produced across the condenser 6 which varies with the magnitude of the sound pulsations and is of a corresponding frequency. The vacuum tube system shown is supplied from a direct current source indicated at 8. The voltage of condenser 6 is impressed upon a control grid of a vacuum tube 9 which may have a screen grid and decoupling circuit It. A condenser H is connected between the filament and plate of tube 9. The constants of this discriminator circuit are so chosen a to amplify those frequencies produced by the passage of a vehicle over the corrugations and to suppress other frequencies. Corresponding voltagesare supplied to the input control grid If the corrugations are spaced apart 1.76

of a vacuum tube l2 through a grid leak l 3 which further suppresses undesired frequency pulsations, and the output of tube I2 is supplied to the input of another tube It through a grid leak l5.

The amplifying tubes l2 and M are operated at complete cutoff as a limiter to produce a square wave voltage of constant amplitude having a frequency corresponding to the sound frequency produced by the corrugations 3. The variable frequency constant amplitude signal controls the input of a detector circuit having a vacuum tube I6 and an output circuit designed to charge a condenser I1 to a voltage proportional to the impulse frequency. Such circuit contains a reactance l8 and a condenser [9 with a rectifier 20 connected across condenser I! from a point between the condenser I 9 and reactance I8. A resistance 2| is connected across the condenser I! so that the charge of this condenser will be removed after the passage of a vehicle over the frequency producing corrugated surface 3 and thus prepare'the detector for detection of the next vehicle. However, durin the passage of a vehicle over the corrugations, the condenser I1 is charged quickly and to a voltage proportional to frequency. This voltage is applied to the input circuit of a tube 22 designed to have an output current closely proportional to its grid voltage and to the signal frequency. The main portion of the output current of tube 22 operates a speed recorder and traffic counter instrument. Such instrument may comprise a recording galvanometer 23 which records on a chart 24, which chart is advanced a predetermined amount for each vehicle passage. As represented, the chart is advanced by a driving drum 25 which is controlled by an escapement having a control allet 26. The escapement pallet is operated in one direction by an electromagnet 2'! in the circuit of galvanometer 23 and in the opposite direction by a spring 28. The drum 25 may be driven by a spring the winding stem of which is indicated at 29. At 30 I have indicated a counter operated by the chart advancing arrangement. Each time a vehicle passes, tube 22 produces an output current which lasts while a vehicle wheel or wheels are passing over the surface 3, and which current is of a magnitude proportional to the vehicle speed. Galvanometer 23 deflects accordingly and pallet lever 26 is attracted to allow the chart to advance a distance corresponding to about one-halt tooth of the escape wheel. As soon as the vehicle has passed, the current output of tube 22 drops to zero and the galvanometer returns to zero position and spring 28 moves the escapement pallet back to detracted position, allowing the driving drum to advance the remaining distance between escapement wheel teeth. Each complete operating cycle of the pallet lever corresponds to the passage of one vehicle and the counter 30 is calibrated accordingly.

The nature of the records obtained is shown in Fig. 2. Thus record 3| may correspond to a vehicle passing at 70 miles per hour and the record at 32 to a vehicle passing at miles per hour. The advancement of the chart only when a vehicle passes makes for economy in the use of chart paper. If the traffic density during different hours of the day is desired, the chart may be advanced by a timing device in which case the nature of the records would appear more as in Fig. 3.

The length of the corrugated strip of highway will preferably be such that with short wheelbase vehicles both front and rear wheels will not be producing the distinguishing sound frequency at the same instant, since this may cause a double frequency sound if the conditions are just right. The consecutive sounds produced by the passage of the front and rear wheels of the same vehicle over the corrugated strip will be so close together that a single operation of the recorder will result.

In Fig. 4, I have indicated a section of highway I having a corrugated strip 3 for registering trafilc in one direction and a strip 3 for registering trafiic in the opposite direction. Such strips should be a sufficient distance apart that a microphone at one strip will not pick up the distinguishing sound from the other strip. Of course, where one is interested only in, the total trafiic in both directions, a corrugated strip extending clear across the road and one microphone may be used.

What I claim as new and. desire to secure by Letters Patent of the United States is:

1. Apparatus for traffic study comprising a corrugated surface adapted to be positioned in a roadway so that vehicles will pass thereover, the corrugations of such surface being uniformly spaced and running across the direction of traffic and of such nature as to produce sound pulsations proportional to the speed of vehicles passing thereover by reason of the vehicle wheel striking said corrugations in succession, a sound responsive pickup receiver positioned in the vicinity of such surface so as to respond to such sound pulsations, an amplifier circuit having its input connected to said sound receiver said circuit being designed to amplify sound pulsations of the frequency range corresponding to that produced by the corrugated surface in response to the passage of vehicles between selected speed limits and to suppress other sound pulsation frequencies, electric supply means for supplying said sound pickup and amplifier circuit, said amplifier circuit producin an output voltage proportional to the frequency of the amplified sound pulsations, and means responsive to such output calibrated in terms of vehicle speed.

2. Trafiic speed responsive apparatus comprising a roadway having a corrugated surface, the corrugations being evenly spaced and lying in a direction across the roadway, such corrugations being of a. nature to emit sound pulsations, when a vehicle passes thereover, of a frequency propor-' tional to vehicle speed, a sound pickup device positioned to respond to such sound pulsations, an amplifier circuit designed to amplify sound pulsations of the frequency range produced by the corrugations due to vehicles passing thereover and to suppress other sound frequencies, said amplifier circuit having an input controlled from said sound pickup device and producing an output voltage proportional to the non-suppressed input frequency sound pulsations, a source of supply for the sound pickup and amplifier circuit, and recording apparatus responsive to the output voltage of said amplifier circuit for recording the speeds of vehicles passing over such roadway.

3. Trafiic responsive apparatus comprising a surface over which vehicles are adapted to pass, said surface being designed to emit sound pulsations of a frequency proportional to the speed of r a vehicle passing thereover, a sound pickup receiver positioned to respond to such sound pulsations, an amplifier circuit havin such sound receiver coupled with its input circuit, said amplifier circuit being designed to produce an output voltage proportional to the frequency of the sound pulsations picked up by said receiver, but

only within a frequency rang selected to correspond to the frequency range of sound pulsations produced by said surface in response to the passage of vehicles moving between selected speed limits, and a recorder responsive to the output voltage of said amplifier circuit for producing a record from which the number and speed of vehicles which pass over such surface within the selected speed limits can be ascertained.

4. Traffic responsive apparatus comprising in combination with a roadway, sound producing apparatus associated with such roadway so as to be operated by the passage of vehicles thereby and to emit sound pulsations of a frequency characteristic of the vehicle speed, a sound pickup device positioned to respond to such sound pulsations, an amplifier circuit for amplifying the sound pulsations picked up by said pickup device but only those sounds which have pulsation frequencies characteristic of the passage of vehicles REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,137,859 Schwartz Nov. 22, 1938 2,218,642 Hathaway Oct. 22, 1940 1,991,060 Osbon Feb. 12, 1935 1,994,232 Schuck Mar. 12, 1935 2,054,787 Beavers Sept. 22, 1936 

